It is well known to form holes of more or less large diameter in thin metallic pieces (sheets) by the principle of coring, that is to say, by tools whose center is free which permits forming a hole by leaving a non-cut volume of material at the center, called the "core."
The known hole-forming tools such as "barrel drills" comprise a helicoidal drill having a central channel for passage of lubricant to permit deep coring. These tools have a number of disadvantages, namely: limited cutting speed due to the substantial pressure forces, rough surface state of the formed holes, large tolerances of the holes, and poor geometry of the obtained holes by the action of the cuttings; the tools also require frequent resharpening.